The invention relates to a radio tuner for coupling with a cassette tape recorder, and more particularly to a radio tuner of the type which is detachably coupled with a cassette tape recorder of a small size.
With the wide-spread use of portable radio sets and increasing miniaturization of cassette tape recorders, a cassette tape recorder with a radio set is available on the market which provides the combined functions of both units. However, the available cassette tape recorder with radio set comprises a combination of the individual units, and therefore has a size which is of the order of several times that of the tape recorder. At best, they are not pocket-size. The present applicant has previously devloped a cassette tape recorder of a miniature size employing a micro-cassette which can be received in the pocket of a shirt. Thus it will be convenient if a radio set can be provided which is detachably coupled with such recorder and which has an overall size substantially comparable to the size of such recorder. This could be accomplished by providing a tuner of a compact form which only incorporates the tuner circuit of the radio set while utilizing the source battery, loudspeaker and amplifier circuit contained within the tape recorder in order to constitute together a composite radio set and which can be detachably coupled with the recorder to form a radio set of pocket-size dimensions. Techniques to achieve such a combined unit are already known. However, to assure a full functioning of a minature tape recorder which represents a precision product, the recorder has a casing formed of a metal material such as aluminium sheet. A problem then arises in that if the tuner casing is formed by a metal, an impinging electromagnetic wave will be shielded from an internally housed antenna, thus preventing or detracting from the effective functioning of a radio set.
The tuner of such a size could accommodate a bar antenna which is utilized to receive an AM broadcast, but cannot accommodate a rod antenna of substantial length which is used to receive an FM broadcast. If the rod antenna is disposed outside the tuner casing, it will detract from the appearance and the pocket-size of the combination comprising the tuner and the tape recorder.
On the other hand, when a radio tuner of the form mentioned above is constructed, considerations concerning the ease of operation, portability and design dictate that a frequency selecting dial be disposed on the major surface of the tuner while an operating knob associated with the dial be disposed on its lateral side. Normally, the dial and the knob are interconnected by a fastening string which is passed around rollers or pulleys interposed therebetween. However, when the dial and the knob rotate in different planes which are at right angles to each other, the fastening string must be diverted in mutually perpendicular directions. This results in a complex arrangement for the construction and mounting of intermediate rollers or pulleys, which cannot be contained within the tuner casing of the small size as mentioned above. Additionally, it becomes extremely difficult to provide a stable and proper motion transmission from the knob to the dial.